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use {
    crate::{
        col_expr::*,
    },
    bet::*,
    lfs_core::*,
    std::{
        str::FromStr,
    },
};

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum BoolOperator {
    And,
    Or,
    Not,
}

#[derive(Debug, Default, Clone)]
pub struct Filter {
    expr: BeTree<BoolOperator, ColExpr>,
}

impl Filter {
    #[allow(clippy::match_like_matches_macro)]
    pub fn eval(&self, mount: &Mount) -> Result<bool, EvalExprError> {
        self.expr.eval_faillible(
            // leaf evaluation
            |col_expr| col_expr.eval(mount),
            // bool operation
            |op, a, b| match (op, b) {
                (BoolOperator::And, Some(b)) => Ok(a & b),
                (BoolOperator::Or, Some(b)) => Ok(a | b),
                (BoolOperator::Not, None) => Ok(!a),
                _ => { unreachable!() }
            },
            // when to short-circuit
            |op, a| match (op, a) {
                (BoolOperator::And, false) => true,
                (BoolOperator::Or, true) => true,
                _ => false,
            },
        ).map(|b| b.unwrap_or(true))
    }
    pub fn filter<'m>(&self, mounts: &'m[Mount]) -> Result<Vec<&'m Mount>, EvalExprError> {
        let mut filtered = Vec::new();
        for mount in mounts {
            if self.eval(mount)? {
                filtered.push(mount);
            }
        }
        Ok(filtered)
    }
}

impl FromStr for Filter {
    type Err = ParseExprError;
    fn from_str(input: &str) -> Result<Self, ParseExprError> {

        // we start by reading the global structure
        let mut expr: BeTree<BoolOperator, String> = BeTree::new();
        for c in input.chars() {
            match c {
                '&' => expr.push_operator(BoolOperator::And),
                '|' => expr.push_operator(BoolOperator::Or),
                '!' => expr.push_operator(BoolOperator::Not),
                ' ' => {},
                '(' => expr.open_par(),
                ')' => expr.close_par(),
                _ => expr.mutate_or_create_atom(String::new).push(c),
            }
        }

        // then we parse each leaf
        let expr = expr.try_map_atoms(|raw| raw.parse())?;

        Ok(Self { expr })
    }
}